1. Field of the Invention
The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the present invention relates to a perforating gun system capable of controlling wellbore fluid dynamics.
2. Description of Related Art
Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.
Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In FIG. 1 an example of a perforating system 4 is shown. For the sake of clarity, the system 4 depicted comprises a single perforating gun 6 instead of a multitude of guns. The gun 6 is shown disposed within a wellbore 1 on a wireline 5. The perforating system 4 as shown also includes a service truck 7 on the surface 9, where in addition to providing a raising and lowering means, the wireline 5 also provides communication and control connectivity between the truck 7 and the perforating gun 6. As is known, derricks, slips and other similar systems may be used for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems may also be disposed into a wellbore via tubing, drill pipe, slick line, coiled tubing, to mention a few.
Included with the perforating gun 6 are shaped charges 8 that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge 8 at very high velocity in a pattern called a “jet” 12. The jet 12 perforates the casing and the cement and creates a perforation 10 that extends into the surrounding formation 2.
As shown in FIG. 2, subsequent to the perforating step, formation fluid flows from the formation 2, into the wellbore 1, and through the annulus 11 formed by the outer circumference of the perforating gun 6 and the inner diameter of the wellbore 1 (the direction of this fluid flow is illustrated by arrows A). Fluid flows from the formation 2 into the wellbore 1 because the wellbore pressure is exceeded by the formation pressure, this is commonly referred to as an under-balanced situation. Debris 14 from the formation however often travels along with the fluid, this debris 14 can sometimes collect within the annulus 11 and in certain locations thereby resulting in a clog 16 that can effectively lodge the perforating gun 6 within the wellbore 1. The connate fluid is shown flowing from within a first zone Z1, into the wellbore 1 into zone Z2. This presents a problem if it is desired to maintain these separate zones (Z1, Z2) at separate pressures.